The present invention relates to the hydrometallurgical extraction of metals, particularly vanadium, niobium, tantalum and zirconium, especially from ores, mineral concentrates and from certain industrial process residues in all of which these metals are associated with other metals. In some cases these other metals constitute undesirable impurities such as aluminum, silicon and iron and in others they constitute commercially valuable materials which are extracted along with vanadium or subsequently to the extraction of vanadium as, for example, in carnotite ores from which vanadium and uranium are coextracted. In this application "industrial process residues" or simply "residues" refers to material remaining after extraction of a primary product in a chemical or hydrometallurgical process. Such residues may be treated as waste products of the process or they may be further extracted to recover one or more constituents of commercial value.
The present invention is especially but not exclusively applicable to the extraction of vanadium from residues obtained in the manufacture of titanium dioxide by the high temperature fluidized bed chlorination (so-called "chloride" processing) of titanium-containing ores such as rutile, ilmenite or leucoxene or ore preconcentrates such as so-called "upgraded ilmenite" or mixtures thereof. Since these ores and ore preconcentrates contain, in addition to titanium, several other elements such as vanadium, zirconium, niobium, tantalum, chromium, iron, aluminum and silicon, the presence of which would be undesirable in the titanium dioxide which is the primary product of the process, they have to be separated and are removed from the plant as residues. These residues also contain a comparatively small proportion of the titanium extracted in the process. Examples of such residues arising from the chorination of rutile to produce titanium tetrachloride are given in U.S. Bureau of Mines Report of Investigation Nos. 7221 (1969) and 7671 (1972). The major components of the residue described are titanium as unreacted rutile and unrecovered titanium tetrachloride, carbon (coke) added in the chlorination process and chlorine as metal chlorides. The impurity metals--vanadium, zirconium, niobium, iron, etc., are present in concentrated form in the residue remaining after distilling off the bulk of the titanium tetrachloride. A typical analysis of the residues appears in the following table.
TABLE I ______________________________________ Percent by Weight ______________________________________ V 4.4 Nb 2.4 Ta 1.1 Zr 2.4 Ti 10.5 Fe 4.2 Cr 1.0 Mn 0.08 Al 2.2 Cl 26.0 C 33.0 SiO.sub.2 4.5 ______________________________________
It will be noted that the remainder of such residues is combined oxygen and minor amounts of other metals.
The recovery of vanadium and niobium from such residues is a commercially desirable objective. Moreover, such residues are difficult to dispose of as waste material since they contain readily hydrolyzable chlorides which generate hydrochloric acid fumes on contact with moisture and also they contain toxic metals, notably vanadium. Thus the so-called "fuming" residues cannot conveniently be stored or dumped in the state in which they are obtained from the extraction process.
In U.S. Pat. No. 3,975,495 to Bowerman a process is described for recovering niobium and vanadium from a solution obtained by aqueous extraction of vanadiferous residues similar to those used in the process of the present invention. In this process the solution containing substantially all the vanadium, niobium and zirconium is separated from the insoluble matter consisting of carbon and unreacted titaniferous ore and subsequently a separation of niobium and zirconium is effected by boiling in presence of sulfuric acid in order to precipitate these metals while leaving vanadium in solution. In the process of U.S. Pat. No. 3,975,495 vanadium is subsequently recovered by oxidation and partial neutralization whereby vanadium and iron are precipitated in a hydrous oxide form, known in the art as "red cake," and are separated from the residual solution by filtration. The recovery of vanadium as oxide or ammonium metavanadate, which are the commercially desirable products, requires further processing which is most usually effected by redissolving the "red cake" in sulfuric acid to form a solution compounded principally of iron sulfate and vanadic acid or vanadium sulfate, from which vanadium is then recovered by solvent extraction or liquid ion exchange. Such extraction processes are well known in the art; for example, one such process is desirable in "COMMERCIAL RECOVERY OF VANADIUM BY THE LIQUID ION EXCHANGE PROCESS" by R. R. Swanson, H. N. Dunning and J. E. House, ENGINEERING AND MINING JOURNAL, October 1961. The process described in U.S. Pat. No. 3,975,495 would be greatly simplified and would consequently be more economical if it were possible to use as a feed solution for the liquid ion exchange process the chloride solution containing vanadium and iron which is obtained after separating insoluble carbon, unreacted ore and niobium and zirconium. By using such a feed solution, the process stages of precipitation of "red cake" and redissolving it in sulfuric acid would thereby be obviated. However, it has not hitherto proved practicable to do this. The reason is that in acid chloride solutions part of the iron contained is present in anionic form, such as FeCl.sub.4.sup.-, and the iron in this form is extracted by the amine or quaternary ammonium compound used to extract vanadium (as vanadate) in the liquid ion exchange process. The result is that a complete separation of vanadium from iron is not achieved. An unsuccessful attempt to achieve such a direct separation of vanadium from iron by direct solvent extraction (or liquid ion exchange) of a chloride solution derived from residues of the chlorination of titaniferous ores is referred to in U.S. Bureau of Mines Report of Invesigations No. 7671.
In my copending application an improved process is described for recovering vanadium from residues of the chlorination of titaniferous ores and from other vanadiferous materials. This process also produces a chloride solution containing vanadium and iron from which vanadium can be recovered in the form of pure vanadium pentoxide or ammonium metavanadate by the conventional procedure of precipitating "red cake," redissolving this in sulfuric acid and separating vanadium from iron by liquid ion exchange. As in the case of the process of U.S. Pat. No. 3,975,495 it would therefore be a desirable objective to separate vanadium from iron by directly applying liquid ion exchange to the chloride solution but, for reasons already stated, this has not hitherto been practicable.